Process of making recycled linerboard or Kraft paper from old corrugated container

Abstract

A process for producing new corrugated containerboard from old corrugated container (OCC) without using expensive virgin UKP includes three new steps. These steps are separating corrugated medium from OCC before pulping linerboard, removing micro-fibrils from defibered linerboard furnish, and minimizing the loss of long fibers through reject streams of fine screens.

What is claimed is:  
     
       1. In a process of making a stock preparation for recycled linerboard or Kraft paper wherein OCC is defibered, cleaned, screened, fractionated into long fibers and short fibers, long fibers being refined to required level of freeness, virgin pulps added to achieve required strength properties, and deposited on a wire and dewatered, the strength properties of the stock are improved by a process comprising the steps of: 
       cutting and/or crushing OCC that contains corrugated medium attached to linerboard into pieces,  
       separating linerboard pieces from corrugated medium pieces,  
       removing any remaining corrugated medium pieces from OCC furnish containing the separated linerboard pieces,  
       adding NaOH to the separated linerboard pieces in the OCC furnish,  
       defibering the separated linerboard pieces in the OCC furnish,  
       eliminating micro-fibrils from long fibers in the OCC furnish,  
       minimizing the loss of long fibers by recovering any long fibers from reject streams,  
       applying dry strength additives to the OCC furnish, and  
       maintaining a furnish pH of from 5.5 to 6.5 at the head box of paper machine.  
     
     
       2. The process of  claim 1  wherein the furnish is a mixture of stock and water and is a pulp recycled from OCC, old Kraft paper sacks, waste paper and mixture thereof. 
     
     
       3. The process of  claim 1  wherein the furnish is a mixture of stock and water and the stock is a pulp recycled from OCC, old Kraft paper sacks, waste paper and mixture thereof, the improvement in strength properties of recycled linerboard or Kraft paper comprising increasing unbleached Kraft pulp content in the furnish by separating linerboard from OCC before pulping OCC. 
     
     
       4. The process of  claim 3  wherein the separation of linerboard from OCC is achieved by breaking OCC into pieces. 
     
     
       5. The process of  claim 4  wherein breaking OCC into pieces is achieved by shredding and cutting OCC. 
     
     
       6. The process of  claim 4  wherein the breaking OCC into pieces is achieved by immersing and agitating OCC in water. 
     
     
       7. The process of  claim 3  wherein, the separation of linerboard from OCC is achieved by defibering corrugated medium pieces first and removing defibered corrugated medium from pulper by the auxiliary pump and/or gate valve. 
     
     
       8. The process of  claim 1  wherein the furnish is a mixture of stock and water and the stock is a pulp recycled from OCC, old Kraft paper sacks, waste paper and mixture thereof, the improvement comprising recovering long fibers from the reject streams of fine screens. 
     
     
       9. The process of  claim 8  wherein the recovery of long fibers from reject streams of fine screens is achieved by non-refining defibering process applied to hornified and/or wet strengthened OCC fractions rejected by fine screens. 
     
     
       10. The process of  claim 1  wherein improvement of stength properties of linerboard or Kraft paper is achieved by increasing unbleached Kraft pulp content in the furnish by increasing the speed of pulper impeller after corrugated medium is removed from linerboard furnish. 
     
     
       11. The process of  claim 1  wherein improvement of strength properties of linerboard or Kraft paper is achieved by maintaining pH at the head box of the paper machine at least 5.5 and at highest 6.5. 
     
     
       12. The process of  claim 1 , further comprising recovering unbleached Kraft pulp by blending of long unbleached Kraft pulp fibers stored in a long fiber tank with short fibers stored in a short fiber tank. 
     
     
       13. The process of  claim 1 , further comprising drying and packaging recovered unbleached Kraft pulp stored in the long fiber tank. 
     
     
       14. The process of  claim 1 , further comprising eliminating micro-fibrils from the recycled furnish is by enlarging holes and/or controlling the rotating speed of screens of a fiber extractor and/or by choosing appropriate hole sizes of fractionators.